The orthesis device according to the invention is specifically designed for the conservative treatment of patellofemoral instability of the knee.
Patellar instability is in fact characterized by a gradual loss of patellofemoral articular alignment, with gradual lateral displacement of the patellar position with respect to the position of the femoral trochlea, which can be classified, depending on the severity of the condition, as follows:
(i) external patellar hyperpressure (the patellar tangential axis is dislocated outward with respect to the axis of the femoral trochlea);
(ii) patellar subluxation (partial loss of articular relationships); and
(iii) full luxation (with complete loss of articular relationships and consequent absolute functional disability).
The cause of the disorder can be found in static alterations, such as a decrease in patellar dysplasia and condylar displasia convexity and/or in the concavity of the femoral trochlea, and in dynamic ones, such as alterations to trophic conditions and to the insertion (lever arm) of the muscles that have a medializing action. The altered patellofemoral alignment is accompanied by an imbalance in the distribution of articular loads, with early wear of the cartilage (covering of the joint surfaces) and becomes clinically manifest with symptoms such as pain, effusions and articulation failures (patellar pseudoseizures). The condition reaches its peak in patellar luxations, where complete loss of articular relationships causes the functional locking of the articulation.
Indications for treatment, defined in relation to an extensive review of the literature, entail:
(1) surgical treatment, electively recommended for recurrent luxations and for minor instabilities which show symptoms despite conservative treatment; and
(2) conservative treatment, including physical therapy, elective strengthening of muscles having a medializing action and stretching of the posterior muscles of the thigh and of the lateral capsular and tendon structures, associated with the use of ortheses.
Conservative treatment can therefore include the use of patellar stabilization ortheses, all of which have the common purpose of restoring normal articular alignment by acting with various methods:
1) patellar centering hole;
2) stabilization system with crossing bands centered on the patella;
3) stabilization system using bands which produce a medializing pressure using traction belts or a presser support.
The drawbacks shown by the ortheses produced so far can be summarized as follows:
1) insufficient medializing action, which fails to produce sufficient alignment of the patellofemoral articulation through flexing and extension;
2) low compliance and limitation of the articulation;
3) pressure due to tangential action which induces an excessive articular load and sustains the associated synovial-capsular inflammation;
4) excessive compressive forces induced on the soft tissues of the posterior region of the knee (muscle and tendon insertions and vascular-nerve structures running in the popliteal area).
The above shortcomings become clinically manifest as:
1) failed reduction of "patellar snapping" occurring on flexing and extension of the knee and produced by contact of the patellar surface with the external "side" surface of the trochlea;
2) difficulty in maintaining an adequate ratio between alignment of the orthesis and the possibility to obtain functional range of motion of the joint for everyday and sports activity of the femur;
3) increase in anterior knee pain, particularly evident in the case of activities which entail marked flexing of the knee;
4) compressive action, which can cause the latency and aggravation of vascular or muscle and tendon disorders in the posterior region of the knee and of the popliteal canal.